When fat cells are extracted from the body, typically in a liposuction procedure, they encompass a range of sizes, from less than 25 microns in diameter, to more than 100 microns in diameter. The smaller cells are typically pre-adipocytes, while the larger cells are fully mature adipocytes. Many of the extracted adipose cells are “alive,” i.e., they survive separation from the surrounding tissue and the extraction process. Information suggests that when the extraction process is performed using ultrasonic assisted lipoplasty (UAL) (such as that performed using the VASER® UAL system commercially available from Sound Surgical Technologies LLC in Louisville, Colo.), a greater portion of the extracted cells are alive and can survive for a limited period of time post-extraction. The extracted cells are of interest in several applications.
In the practice of medicine, it is sometimes desired to re-inject the extracted adipose cells into the same patient for purposes of filling or augmenting body locations, e.g., plastic surgery, body sculpting or enhancement. To optimize that process it is helpful to re-inject only live cells. Further, it would be preferable to inject only the smaller cells, preferably the pre-adipocytes. This is because the pre-adipocytes more readily adapt to the re-implantation process, and also stimulate the production of the vascular structure necessary for successful grafting, through the expression of vascular growth factors. The more mature cells, on the other hand, do not generally express the vascular growth factors, and are more likely to undergo necrosis after re-implantation. It is therefore desirable to separate the mature fat cells from the liposuction aspirate before re-implantation. Further, it may be desired to destroy the mature fat cells, so that the only viable cells remaining are of the smaller, more active type. While an exact cut-off size which is optimal for re-insertion has not been clinically established, generally, it would be desirable to lyse those cells larger than about 50 microns. However this may be considered on a patient-by-patient basis, for instance, depending upon the total amount of fat available for re-implantation, the amount required to be re-implanted in order to produce the desired result, the general condition of the patient's cells, etc.
Secondly, it has now been found that stem cells can be derived from adipose cells, a discovery having significant implications for medical research regarding both humans and animals. (See, for example, U.S. Pat. No. 6,777,231 for “Adipose-Derived Stem Cells and Lattices,” issued on Aug. 17, 2004.) Young adipose cells are prime candidates for the derivation of stem cells. Stem cells are generally in the range of 15-25 micron in diameter.
Stem cells can be used to regenerate human or other animal tissue. Once isolated, stem cells can be reintroduced into a human or other animal to regenerate tissues, in vitro. Because stem cells may be reintroduced into a human body, processing performed to isolate the stem cells must be performed in a sterile environment.
Thus, it would be desirable to be able to isolate the younger, smaller cells from adipose tissue extracted from humans and other animals and easily maintain a sterile environment for the stem cells to be safely re-injected into a patient.
It is further desirable that this selection, separation, and/or destruction process be accomplished in a rapid manner, as the time between “aspiration” (i.e., removal of tissue from the body via suction) and re-implantation or storage for research should be kept to a minimum.
Prior efforts in this area have involved centrifugation, which does not precisely segregate cells of different sizes. Successful centrifugation also requires a precise drawing off of the centrifuged material, which requires additional handling. Filtering of the aspirate is also possible, although this can also be a time consuming process, and can also cause damage to the cells of interest as they pass through the filter material. Also, since cells are often aggregated in the aspirate and not singulated, it is likely that a cluster of the desired, smaller cells would be filtered out. For example, a cluster of more than a few 50 micron diameter cells would be filtered out by a filter with a 150 micron mesh, which defeats the purpose of the entire filtering process. The use of filtering and/or centrifugation also requires the use of additional devices that must be sterilized to avoid contaminating the stem cells.
Thus, neither centrifugation nor filtering has completely solved the problem of isolating smaller, younger adipose cells. Centrifugation does stratify the aspirate material, with smaller, denser cells at the bottom, and larger, less dense cells at the top of the centrifuge tube. However, the stratification is imprecise; it can be affected by clustering of the cells; and it can cause damage to the desired cells by both additional handling and the stresses of centrifugation.
Similarly filtering the aspirate is also imprecise in that the tendency of cells to be in clusters affects the filtering process.
Accordingly, a need still exists for an improved method of isolating younger adipose cells from an aspirate mixture and maintaining the sterility of the aspirate mixture.